The present invention relates to a flame retardant silicone fluid composition or, more particularly, to a flame retardant silicone fluid composition which can be used as an insulation oil in electric equipment with high safety by virtue of the excellent flame retardancy and self-extinguishability imparted thereto without affecting the electric properties and heat resistance.
Various kinds of oily materials are known and used as an insulation oil in electric equipments such as electric power cables, capacitors, transformers and the like including mineral oils, phosphate ester oils, aromatic hydrocarbon oils, chlorinated synthetic oils, silicone fluids, fluorocarbon oils and the like. These conventional insulation oils have their respective problems and disadvantages from the standpoint of practical use. For example, mineral oils, aromatic hydrocarbon oils and low-viscosity silicone fluids are inflammable and chlorinated synthetic oils and notoriously toxic while fluorocarbon oils have a problem of unduly increasing the weight of the electric equipments filled therewith due to the outstandingly high specific gravity thereof in addition to the impractical expensiveness.
Silicone fluids having a high viscosity of, for example, about 50 centistokes or higher at 25.degree. C. are self-extinguishable and have a relatively high flash point so that they can be more flame retardant than the above named insulation oils of other types. The high-viscosity silicone fluids, however, not always can be fully flame retardant and are not usable as a highly reliable flame retardant insulation oil because different methods for the evaluation of the flame retardancy thereof may give different results. To explain in more detail, namely, flame retardancy of insulation oils are evaluated by several different methods including the flash point method, ignition point method, oxygen index method, glass tape method and the like of which the horizontal glass tape method specified in JIS C 2101 may be the most reliable method although a program sponsored by IEC is now under progress to establish a reliable testing method for the evaluation of the flame retardancy of various electric insulation oils. When high-viscosity silicone fluids are tested by the horizontal glass tape method, in which a tape of woven glass fibers is soaked with the silicone fluid and held horizontally to be ignited, they can be classified to the class of flame retardant insulation oils while they are no longer flame retardant when tested by the vertical glass tape method, in which the silicone fluid-soaked glass tape is held vertically to be ignited.
Flame retardancy of a silicone fluid can be enhanced by admixing the fluid with a flame retardant agent and several compounds are proposed as a flame retardant agent in, for example, Japanese Patent KokaiNo. 57-28157 and Japanese Patent Publications Nos. 49-39173, 51-20720 and 59-226408. None of the flame retardant agents in the prior art, however, is fully effective for rendering a silicone fluid flame-retardant.